1. Technical Field
The present invention relates to printed circuit boards, particularly to a method for manufacturing printed circuit boards.
2. Description of Related Art
Printed circuit boards are widely used in electronic products for electrical connection. Typically, printed circuit boards are manufactured using a series of wet processes (i.e., processes of treating printed circuit boards with treatment liquids). The wet processes generally include coating a photoresist layer on a copper layer of a copper clad substrate, developing the photoresist layer to form a patterned photoresist layer, etching the copper layer exposed from the patterned photoresist layer to form electrical traces, removing the patterned photoresist layer, and so on.
However, during the processes of manufacturing printed circuit boards, the surfaces contacting with the treatment liquids (e.g., a surface of the copper layer of the copper clad substrate, a surface of the photoresist layer, etc.) usually has some performance defects due to contaminations or oxides thereon. Thus, the surfaces have a large liquid contact angle. In the aforementioned wet processes, when the treatment liquids contact with the surfaces, an affinity of the treatment liquids to the surfaces is poor which result in the treatment liquid not being able to spread on and wet the surfaces completely. The treatment liquids act on the surfaces in a low efficiency. Therefore, quality of the printed circuit boards manufactured using these wet processes is low.
For example, in the wet process of coating the photoresist layer on the surface of the copper layer of the copper clad substrate, a liquid photoresist is applied on and contact the surface of the copper layer. The surface of the copper layer generally has a large liquid contact angle due to an oxidation film formed thereon and organic contaminations deposited thereon. During the wet process of applying the liquid photoresist on the surface of the copper layer to form the photoresist layer, an affinity of the liquid photoresist to the surface of the copper layer is poor. Thus, the liquid photoresist cannot spread on and wet the surface of the copper layer completely, thereby forming a barrier layer between the liquid photoresist and the surface of the copper layer. Because of the barrier layer, the photoresist layer formed cannot contact the surface of the copper layer tightly. As a result, the patterned photoresist layer formed on the basis of the photoresist layer may has a poor precision.
Furthermore, in the wet process of developing the photoresist layer, a developing agent contacts the surface of the photoresist layer and reacts with the photoresist of the photoresist layer. Because the surface of the photoresist layer is usually smooth and has a large liquid contact angle, an affinity of the developing agent to the surface of the photoresist layer is poor which results in the developing agent not being able to spread on and wet the surface of the photoresist layer. Thus, the developing agent reacts with the photoresist in a low efficiency, which even causes to form the patterned photoresist layer with a poor precision. As a result, the electrical traces formed on the basis of the patterned photoresist layer may also have a poor precision, thereby affecting quality of the printed circuit board.
What is needed, therefore, is a method for manufacturing printed circuit boards so as to improve the performance of the surface of a copper clad substrate, thereby improving quality of the printed circuit board using the copper clad substrate.